1. Field of the Invention
This invention relates to material storage and transfer facilities for bulk granular and powdered material storage. More particularly, the present invention relates to an improved support structure for the rotating center column and auger transfer apparatus typically used in dome storage structures.
2. State of the Art
Many granular and powdered bulk materials require a controlled storage environment and unique handling profile during loading and unloading in storage areas. For example, grain, portland cement, fly ash, dry fuels, and other such commodities must be totally enclosed and protected from the elements when stored. However, the total enclosure of bulk materials limits convenient access for retrieval, making quick and complete reclamation difficult. Although movable roofing permits direct use of scoop shovels and buckets to raise the material to nearby trucks or railcars, such facilities and methods are labor intensive and require a significant capital investment for equipment and special construction of buildings.
There are many well known methods for the storage and retrieval of such materials. One method that has gained widespread popularity in recent years is the use of dome structures for storage. Free-standing dome structures, such as disclosed in U.S. Pat. No. 3,456,818, are extremely strong and space efficient, requiring a minimum of materials to obtain a large volume of enclosed space. They are also relatively inexpensive to construct as, for example, by thin-shell concrete balloon forming methods.
Additionally, reclamation of materials from an enclosed storage location may present significant challenges due to the nature of the material. For example, dry portland cement settles and compresses when stored, creating a compact and dense mass that can be difficult to remove. If this material is sought to be removed by a front-end loader through lateral doors at the base of a storage enclosure, the compressed cement may not readily collapse with removal of under-supporting material, allowing the creation of a sizable cavern within the material. This cavern could collapse suddenly, with disastrous results.
To solve these sorts of problems, automated reclamation devices for use within domed material storage structures have been developed. For example, U.S. Pat. No. 5,449,263 and prior patents disclose a free-standing domed storage structure having a mechanical reclaimer installed therein. Such a system is shown in FIG. 1. These reclaimers typically comprise a rotating vertical column 16 in the center of the dome storage structure 10, with one or more elongate material transfer structures 40 and 41 attached thereto. These transfer mechanisms are necessarily shorter than the radius of the dome so as not to contact the inside surface of it. The transfer mechanisms typically employ auger devices 17 and 18 to move material, and are usually attached to a bridge type structure that is attached to the bottom of the column via a hinge 42, and connected to the top of the column via a cable 61 and winch device. The column is rotated by a drive motor 60 located at the top of the center column, with auger drive motors 62 positioned at the distal ends of the transfer structures. The cable 61 and winch mechanism allows the transfer structures to be selectively raised or lowered to contact the surface of the stored material.
The domed storage structure is typically filled via a conveyor 12 or similar transport mechanism that drops material into the dome through an opening 13 in the top center. Upon filling, the center column and transfer mechanism are designed to be buried in the stored material with the elongate transfer bridge retracted to an upright position as shown. When the material is to be reclaimed, sufficient quantity of material is removed from the dome by some means that allows pure gravity flow of the material into an outlet opening 19. Then the transfer bridge structures 40 and 41 are lowered to the material surface, and as the column slowly rotates about its central axis 22, the augers sweep and drag the stored material toward the bottom center of the interior of the dome in a gradually declining conical motion, where, at the base of the column, some means is employed to gather the material and transport it under the floor of the dome. Such gathering and transporting mechanisms have in the past employed a gathering chute 24 directly beneath the center column, which drops the material onto a conveyor belt system 82 in a tunnel 80 beneath the dome floor, as shown in FIG. 1.
However, this typical arrangement presents several problems that have not previously been solved in the industry. The center column of these material storage facilities imposes enormous structural loads at its base due to its own weight and the weight of the transfer mechanisms attached thereto. For example, typical storage domes may be upwards of 100' tall, having a 48" diameter steel center column, with a very large rotational drive motor and gear box mounted on top, and substantial appurtenant structures such as maintenance platforms, hatches, ladders, hinged bearing, and winches, etc., in addition to the transfer mechanism bridges and their drive motors. Additionally, the weight of the stored material imposes even more significant loads upon the column and transfer bridges. For example, as dry cement is poured into the structure, it settles on all exposed surfaces of the column, transfer structure, and auger blades. Because it settles naturally through the air in the dome, at first the cement is light and aerated. However, as the cement piles up, its weight compresses the layers underneath. This gradual compressing and densification of the cement causes it to impose a substantial portion of its weight on the exposed surfaces of the column, transfer structure, and especially the auger blades which present nearly horizontal surfaces when the transfer structure is in the upright position. Thus a significant portion of the weight of the stored material is borne by the center column, instead of the floor of the dome. The inventors have calculated that loads imposed by the center column in such structures may exceed 1.5 million pounds.
The magnitude of the column loads causes a problem for transfer of the granular or powdered material into the subsurface conveyor. The column necessarily passes through the center of the dome, which is also the focal point to which the transfer augers drag the material. In past structures, the center column is supported on massive vertical structural plates crossing at right angles through the center of the column, which are in turn supported at their perimeter on massive steel beams. These beams are then supported by the walls of an underground tunnel or other foundation providing support at the corners of a square or similar arrangement. The crossed plates and perimeter support provide for an opening essentially through the center of the column at its base, into a chute that is coaxial with the column, yet has no center obstruction. The material can then drop onto a conveyor which passes beneath the center of the column between the tunnel walls or other foundation which supports the column. This arrangement allows for satisfactory handling of the material, but is extremely expensive and labor intensive to construct. It would be advantageous to have a means of supporting the center column which allows the column to transmit its heavy structural loads more directly into its foundation, yet still allow the easy gathering and transport of the granular or powdered material at the base of the column.
Additionally, the weight of the stored material imposes significant loads on the conveyor tunnel beneath the floor of the structure. Such tunnels may be 10' to 12' tall, and equally as wide in order to accommodate the conveyor equipment and maintenance personnel as needed. Because of this size, the tunnels are expensive to construct due to the significant structural loads that must be borne. It would be advantageous to incorporate a material conveyor means into such domed storage structures that does not require such a large subsurface tunnel so as to reduce the cost and complexity of the structure.